Determined diffuser devices of active substances, used as air fresheners, insecticides and the like, are based on the heating of the active substance contained in the actual diffuser device, so that the evaporation of said substance permeates the surroundings in which the device in question is located.
This type of device can come with a plug forming an integral part thereof so that in this particular case it is applied directly in an electric plug socket. In general, heat is released by means of an exothermic process based on a heater element included in the diffuser device. With this the heating takes place of the volatile substance contained in the diffuser device, which gives rise to the evaporation of said substance. For this reason, it is convenient to refer in a general manner to that kind of active substance diffuser device as “thermodiffuser”.
Such active substance thermodiffusers are marketed in some cases with no indicator whatever as to whether they are releasing heat or not, whereby it is not known whether the device is fulfilling its diffusion function or not, unless it is touched and it is observed by touch whether or not it is hot, assuming that if it is hot the device is diffusing and if it is cold the device is not diffusing.
In the particular case in which these active substance thermodiffusers have a plug for the supply of electric power to a heater, they can moreover be marketed with a luminous indicator, generally a light-emitting diode (hereinafter a LED), so that if said LED is on, it indicates that the thermodiffuser is being fed electrically, but not with certainty that the heating being produced is characteristic of its correct operation.
There is a third type of active substance thermodiffuser whose operation is determined either by the position of an electric switch which can be light-emitting or not, or by the relative position of one or more than one moving piece which forms part of the design of the device and acts as an electric switch.
In all cases, and specifically in those in which there is a light-emitting indicator or indicator of another type to signal the supply of power, it is known if the device is being fed electrically, but it is not known if evaporation of the active substance is taking place by means of heating.
On the other hand, thermochromic elements are known applicable as informative means or as indicators of the temperature of certain devices. In this sense mention can be made of the European Patent with Publication Number 0294136, in which a heating unit is described with thermochromic indicator of the temperature, wherein the indicator includes an electrically resistant thick film indicator track, with a defined configuration printed on a substrate of a layer of thermochromic material applied to the substrate to cover and surround the defined configuration. For its part, the heating unit includes elements to respond to the current flowing through the heating element, generating a current in the indicator track. Consequently, when the element heats up, so too the indicator track, an area of colour change being visible which shows the defined configuration.
Likewise, mention can be made of the European Patent with Publication Number 0287336 with respect to one a heating unit with thermochromic region which comprises a warmable surface with a region of that surface coated or provided with a layer which has a thermochromic material in sufficient quantity to be affected by the received heat, the thermochromic material having a limiting wavelength of absorption which changes reversibly with temperature in the range from 20 to 400° C., at least. The absorption wavelength limit is at least 540 nm at 20° C. and increases progressively up to 700 nm at 400° C. This heating unit can provide a visible indication of whether the warmable surface is or is not yet hot when the electric power has been disconnected.
Likewise, mention can be made of the Spanish Patent with Publication Number 2147513, with respect to a temperature indicator system which comprises a support which is printed with one or more thermochromic inks and which is coupled to a temperature indicator scale, which is calibrated according to the characteristic temperature of the inks mentioned. The system is based on printing the aforementioned support with a band of ink, thermochromic or not thermochromic, on which are printed in turn windows of whatever form, placed successively with a thermochromic ink of characteristic temperature different to that of the band. This indicator system is applicable in the production of devices which can be adapted to containers of products the temperature of which should be controlled in a continuous manner.
Mention could also be made of the Spanish Patent with Publication Number 2137129 with respect to a procedure to obtain the chromatic variation of objects, in the presence of external stimuli and product obtained thereby.
In any case, no non-electric indicators of operation of an active substance thermodiffuser device are known, based on the thermochromic property of certain products.